text: /*******************************************************************************
  * Copyright 2002-2020 Intel Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *******************************************************************************/
  
  /* 
  //               Intel(R) Integrated Performance Primitives
  //                   Cryptographic Primitives (ippcp)
  // 
  //  Contents:
  //     ippsSub_BN()
  // 
  */
  
  #include "owndefs.h"
  #include "owncp.h"
  #include "pcpbn.h"
  #include "pcptool.h"
  
  
  /*F*
  //    Name: ippsSub_BN
  //
  // Purpose: Subtract BigNums.
  //
  // Returns:                Reason:
  //    ippStsNullPtrErr        pA  == NULL
  //                            pB  == NULL
  //                            pR  == NULL
  //    ippStsContextMatchErr   !BN_VALID_ID(pA)
  //                            !BN_VALID_ID(pB)
  //                            !BN_VALID_ID(pR)
  //    ippStsOutOfRangeErr     pR can not hold result
  //    ippStsNoErr             no errors
  //
  // Parameters:
  //    pA    source BigNum
  //    pB    source BigNum
  //    pR    resultant BigNum
  //
  *F*/
  IPPFUN(IppStatus, ippsSub_BN, (IppsBigNumState* pA, IppsBigNumState* pB, IppsBigNumState* pR))
  {
     IPP_BAD_PTR3_RET(pA, pB, pR);
  
     IPP_BADARG_RET(!BN_VALID_ID(pA), ippStsContextMatchErr);
     IPP_BADARG_RET(!BN_VALID_ID(pB), ippStsContextMatchErr);
     IPP_BADARG_RET(!BN_VALID_ID(pR), ippStsContextMatchErr);
  
     {
        cpSize nsA = BN_SIZE(pA);
        cpSize nsB = BN_SIZE(pB);
        cpSize nsR = BN_ROOM(pR);
        IPP_BADARG_RET(nsR < IPP_MAX(nsA, nsB), ippStsOutOfRangeErr);
  
        {
           BNU_CHUNK_T* pDataR = BN_NUMBER(pR);
  
           IppsBigNumSGN sgnA = BN_SIGN(pA);
           IppsBigNumSGN sgnB = BN_SIGN(pB);
           BNU_CHUNK_T* pDataA = BN_NUMBER(pA);
           BNU_CHUNK_T* pDataB = BN_NUMBER(pB);
  
           BNU_CHUNK_T carry;
  
           if(sgnA!=sgnB) {
              if(nsA < nsB) {
                 SWAP(nsA, nsB);
                 SWAP_PTR(BNU_CHUNK_T, pDataA, pDataB);
              }
  
              carry = cpAdd_BNU(pDataR, pDataA, pDataB, nsB);
              if(nsA>nsB)
                 carry = cpInc_BNU(pDataR+nsB, pDataA+nsB, nsA-nsB, carry);
              if(carry) {
                 if(nsR > nsA)
                    pDataR[nsA++] = carry;
                 else
                    IPP_ERROR_RET(ippStsOutOfRangeErr);
              }
              BN_SIGN(pR) = sgnA;
           }
  
           else {
              int cmpRes= cpCmp_BNU(pDataA, nsA, pDataB, nsB);
  
              if(0==cmpRes) {
                 ZEXPAND_BNU(pDataR,0, nsR);
                 BN_SIZE(pR) = 1;
                 BN_SIGN(pR) = ippBigNumPOS;
                 return ippStsNoErr;
              }
  
              if(0>cmpRes) {
                 SWAP(nsA, nsB);
                 SWAP_PTR(BNU_CHUNK_T, pDataA, pDataB);
              }
  
              carry = cpSub_BNU(pDataR, pDataA, pDataB, nsB);
              if(nsA>nsB)
                 cpDec_BNU(pDataR+nsB, pDataA+nsB, nsA-nsB, carry);
  
              BN_SIGN(pR) = cmpRes>0? sgnA : INVERSE_SIGN(sgnA);
           }
  
           FIX_BNU(pDataR, nsA);
           BN_SIZE(pR) = nsA;
  
           return ippStsNoErr;
        }
     }
  }
  